WO1994020679A1

WO1994020679A1 - Security paper comprising localised areas with reduced thickness and opacity, and method for making same

Info

Publication number: WO1994020679A1
Application number: PCT/FR1994/000225
Authority: WO
Inventors: Pierre Doublet; Yves Douesneau; Jean-Paul Menez
Original assignee: Arjo Wiggins S.A.
Priority date: 1993-03-02
Filing date: 1994-03-01
Publication date: 1994-09-15
Also published as: EP0687324B1; EP0687324A1; ES2142937T5; DE69422705T2; ES2142937T3; DE69422705T3; EP0687324B2; DE69422705D1; US6402888B1

Abstract

A method for making a paper sheet comprising at least one region which is thinner than the rest of the sheet. According to the method, a first paper layer (3) is formed on a wire in a first wet end of a paper-making machine, a second paper layer (5) is formed on a wire in a second wet end of the paper-making machine, one of the two paper layers has a number of localised thinner regions (8) so that the thickness (e2) of said paper layers in said regions is up to 50 % less than the thickness (et) of the rest of the sheet, and the two layers are joined together and dried. The resulting paper may be used in banknotes or cheques.

Description

SECURITY PAPER HAVING LOCALIZED AREAS OF REDUCED THICKNESS AND OPACITY AND MANUFACTURING METHOD THEREOF

The invention relates to a sheet of security paper comprising localized areas of reduced thickness and opacity, and more particularly to a banknote paper or a security paper comprising large areas of reduced thickness and opacity, specific locations, these areas being watermarks.

The invention preferably relates to a sheet of paper comprising at least one zone having a uniform average opacity less than at least 40% compared to the opacity of the rest of the sheet.

In the present description, "paper" means any sheet obtained by the wet process using a suspension of natural cellulose fibers and / or synthetic fibers which may contain various fillers and various additives commonly used in stationery.

Papers which are transparent! Ses are already known in the prior art. These papers are for example made transparent by chemical compositions (see in particular French patent n ° 8205124, filed on March 15, 1982 by ARJOMARI-PRIOUX). These papers are made transparent over their entire surface and are intended for applications for industrial design, reproduction of plans, etc.

Chemical processes of partial transparency are also known, that is to say at specific locations. These methods use compositions based on grease or mineral or vegetable oil which are deposited by printing. However, it is difficult to print on these transparent areas using current conventional printing techniques (offset, intaglio, photogravure, etc.).

Furthermore, it is known to make differences in thickness and density in the paper, in particular by the watermark technique used to secure papers for banknotes, identity documents or official and valuable documents. These watermarks are obtained during the manufacture of the sheet of paper by round shapes comprising hollow and / or relief imprints or by means of watermark rollers comprising hollow and / or relief drawings associated with a flat table. (Fourdrinier machine). One then obtains an image which, when looking at the sheet of paper in transmission, appears either clear, if the watermark roller has a relief design, or dark, if the watermark roller has a hollow design. The light areas are due to the fact that the sheet thickness and the density of the fibers are smaller than the sheet thickness and the density of the fibers in the areas where the watermark has not been imprinted . On the contrary, the dark areas are due to the fact that the thickness of the sheet and the density of the fibers are greater.

Such watermarks have clear parts which generally have areas of a few mm ² and the variation in opacity between the light part of the watermark and the non-watermarked paper is small. If you want to print on the light areas of these watermarks, it is very difficult to match the light areas and the printing and even with very precise identification of the watermarks, it is difficult to obtain a good match.

We have described in European patent application No. 388090, filed March 9, 1990 by DE LA RUE COMPANY PLC. a security paper comprising zones of reduced opacity, at determined and well-localized locations, the zones making it possible to see by transmission, with the naked eye, prints carried on the face opposite to the face on which we are looking at the paper . The zones can, for example, be produced in the form of a watermark by using methods of round shape or with watermark rollers.

However, in this patent application, we do not describe how these zones are obtained industrially.

Industrially, it is relatively easy to manufacture paper comprising areas of reduced thickness and therefore clear, obtained by the watermark technique, when the area of these areas is less than 0.4 cm ² . On the other hand, if one wishes to obtain zones whose surface is greater than 0.4 cm ² , by the technique of the watermark the skilled person encounters technical problems.

The first problem is as follows: To make a watermark, the skilled person knows that one can work the canvas in a round shape using a punch. For example, if you want a clear circular area, emboss the canvas with a circular punch. However, using such a method, one does not obtain a clear zone of constant opacity. Indeed, it has been observed that the fibers tend to deposit in greater quantity in the vicinity of the center of the embossed part than on the edges and therefore the center of the watermark appears much less clear than the edges. If we use a watermark roll which has raised asperities, we get the same phenomenon.

A second problem which arises is that when one wants zones of reduced thickness and therefore clear having an area of more than 0.4 cm ² , one does not obtain a clear zone.

In addition, various means are known to avoid forgery of checks. Thus, chemical compounds which react with acids, bases or erasers can be added to or on the check paper. However, we are always looking for new means against falsification.

There has been described in the European patent application filed on November 18, 1992 by the applicant and published on June 30, 1993 under the number EP-A-539384, a method of manufacturing a sheet of paper comprising at least one zone having a thickness reduced compared to the thickness of the rest of the sheet, and having an area of at least 0.4 cm ² , by placing on an embossed or unembossed canvas, possibly arranged on a round shape, an aqueous dispersion containing at least cellulosic fibers, by draining the water to form the sheet, with or without the presence of a watermark roller, while drying. Flexible parts are used which are combined with the watermarked canvas, the watermark roller or the round shape, so that the dripping of water during the formation of the sheet in the areas of the flexible parts is reduced compared to the water dripping in areas with no flexible parts.

The sheet of paper obtained according to this process is such that the zone having a reduced thickness has a thickness less than 40% of the thickness of the rest of the sheet. The sheet may also be such that said zone has an average opacity less than 40% of the opacity of the rest of the sheet. Such a method therefore makes it possible to obtain zones of reduced opacity. However, efforts are still being made to reduce the opacity of the zones.

In addition, the process requires a transformation of the paper machine, that is to say that Ton associates with the watermarked fabric, or with the watermarking roller, or in the round shape, flexible parts. These parts must be fixed in specific locations and therefore require additional handling. In addition, the area has a thickness 30% less than the thickness of the rest of the sheet.

Banknotes are also known which consist of sheets of transparent synthetic material on which a two-sided printing is carried out, the printing being such that it leaves a completely transparent area. On this transparent area, a hologram is reported. Such plastic tickets, however, have some drawbacks. They are not very resistant to handling and traffic because the print can be fragile on the plastic. This is why we prefer paper tickets, but at the same time we want to make the area as transparent as possible. However, according to the method described in document EP-A-549 384, the area obtained is certainly of reduced thickness and reduced opacity, but an area of even lower opacity is desired.

Consequently, another object of the invention is to produce a practically transparent or translucent area in the paper, without piercing the paper in this area.

Another object is to provide a practically transparent or translucent zone in the paper, this zone which can be printed and / or which can receive a hologram or any other distinctive or security mark.

This zone must therefore be strong enough to support the carrying of a safety mark.

An object of the invention is therefore to provide zones of reduced thickness compared to the rest of the sheet without the need to use associated flexible parts.

Another object of the invention is to provide zones having a thickness lower much more reduced than 40% compared to the rest of the leaf.

To this end, the invention relates to a sheet of paper comprising at least one zone of reduced opacity, that is to say a zone having a uniform average opacity less than at least about 40% compared to the opacity from the rest of the sheet, the area having an area of at least 0.4 cm ² , characterized in that the area has a reduced opacity due to the reduction in its thickness compared to the thickness of the rest of the sheet and the fact that it has undergone additional transparency.

The sheet according to the invention may comprise in a part of the zone of reduced opacity a hologram, an iridescent coating, a printing using conventional inks or inks containing colored pigments, fluorescent pigments, luminescent pigments, compounds photochromes, piezooptics, piezochromes.

The sheet of paper may be a single-ply or single-ply sheet, that is to say a sheet comprising an area whose thickness is not zero, the residual thickness being chemically transparentized.

According to another embodiment, the sheet of paper can be a twin-ply sheet or two layers, that is to say that it consists of a first jet or layer comprising an area whose thickness is zero, and a second spray partially or completely transparentized. In the case where the second jet is completely transparent, this jet can be obtained according to the tracing paper technique, namely from a suspension of very refined cellulose fibers, to obtain transparency. In the case where the second jet is partially transparent, it is chemically transparent in an area which comes into correspondence with the zone of zero thickness of the first jet.

The invention further relates to a method of manufacturing a sheet of paper comprising at least one region having a thickness reduced compared to the thickness of the rest of the sheet, characterized in that:

a first layer of paper is formed on a canvas of a first wet part of a paper machine,

- a second layer of paper is formed on a canvas of a second part wet from a paper machine,

- One of the two layers of paper having at least local regions of smaller thickness, so that the thickness of the two layers of paper in said regions is up to 80% relative to the thickness of the rest of the leaf,

- the two layers are combined and dried.

One or even two layers of paper can be produced without problem so as to be locally very thin, at least one of the layers of paper in a region being reduced locally so that the overall thickness of the two layers is sufficiently reduced to obtain a good transparency.

Although the layers of paper are produced on separate paper canvases, a sheet of paper is obtained which it is no longer possible to separate due to the rapid coupling of these layers and their joint drying. The sheet of paper is no different from a sheet of paper made on a single canvas.

The process is such that the regions of smaller thickness in the paper layer (s) are produced by embossed regions in relief on the mechanical fabric, where it follows that the deposition of fibers in these regions is reduced or totally prohibited .

Preferably at least one of the layers of the paper is produced by a machine with a round shape.

More preferably, one of the two layers may include regions in which the thickness is zero.

The thinner regions of the paper strips are formed in the form of a simple geometric pattern, in particular in the form of flat regions which are approximately rectangular, round or elliptical or any other shape.

The following description, with reference to the accompanying drawings by way of nonlimiting examples, will make it possible to understand how the invention can be put into practice. FIG. 1 shows a device which can be used for manufacturing security paper according to the invention.

Figures 2, 3 and 4, 5 and 6 show in section various papers produced according to the invention.

Figure 7 shows a check paper obtained according to the invention.

Figure 1 shows a device that can be used to make a paper according to the invention. The device essentially corresponds to the usual commercial paper machines, which comprise at least two separate wet parts. The preferred embodiment shown here is constituted by a combination of two round-shaped wet parts 1 and 2 of a so-called double-round paper machine. In the wet part 1 a first strip of paper 3 is produced, which is directed towards the second wet part 2 while being suspended below the pick-up felt 4. In the second installation 2 a second strip of paper 5 is produced. Both strips of paper are brought together at the roller 6 and are then dried.

Two round-shaped installations are preferably used for the production of the two layers of paper. However, it is also possible to produce the two layers of paper in flat table installations, or to use a combination of a flat table installation and a round-shaped installation for making the two layers of paper. Finally, only a round shape can be used and in this case the sheet is made transparent in the areas of reduced thickness.

In Figures 2 and 3, there is shown a paper according to the invention. This sheet 7 is formed by a first strip 3 and a second strip 5. The strip 5 comprises clear watermarks 8 obtained for example by an embossing in relief of the canvas of the round shape 5. These clear watermarks have a depth e- ,. The total thickness e _t of the sheet 7 is the sum of the thicknesses e ₃ of the strip 3 and e ₆ of the strip 5. The thickness e ₂ of the sheet 7 opposite the watermarks 8 is less than the total thickness and _t . In Figure 2, we have, = 1/3 e _t = 33.3% e _t .

In Figure 3, we have, = 1/2 e _t = 50% e _t . In FIG. 4, the region 8 is such that the strip 5 has a hole.

The reduction in thickness is therefore approximately 33% in the first case and 50% in the second case. The sheet of Figure 3 therefore has a reduced opacity much lower than the opacity of the sheet of Figure 2, in the region 8 and this for a total thickness e _t substantially equal.

By adjusting the thickness e ₃ and e _B of the strips 3 and 5, as well as the depth e, of the watermarks 8, it is possible to obtain the reduced opacities and thicknesses which one desires.

The sheet shown in Figure 5 is produced using the monojet technique. This sheet is obtained by the process described in application EP-A-549384.

The sheet 11 comprises zones 12, 12a, 12b, of thickness e, and zones 13, 13a, of thickness e ₂ not zero. The zones 13, 13a have a density of fibers much lower than the density of the zones 12, 12a, 12b. Each zone 13, 13a undergoes an additional transparency. This transparentization is carried out chemically according to this embodiment. Preferably, the transparentization is carried out using a transparentization composition described in the European patent of the applicant EP-91 341. The additional transparentization is carried out after drying of the sheet, at the end of the machine.

This composition can for example consist of:

12% of a modified ketone - aldehyde condensing resin 23% of a hexamethoxymethylmela resin 4% ethyl alcohol 17% butyl alcohol 28% dibutylphthalate 16% isopar affinic products.

This composition is applied for example by printing using an engraved printing cylinder, the cylinder engravings corresponding to the areas 13, 13a to be transparentized.

FIG. 6 represents in section a sheet 14 obtained according to the technique of "bijet" shown in Figure 1.

The sheet 11 shown in Figure 6 is formed of a first strip 16 and a second strip 17. The strip 17 is such that it has zones 18 of zero thickness. The strip 16 may or may not be transparentized in the zones situated opposite the zones 18. The strip 17 may also have zones 18 of non-zero thickness which are then clear watermarks obtained for example by an embossing in relief of the canvas the round shape 5. Likewise, in this case, the strip 16 may or may not be made transparent in areas facing the areas 18.

The zones of zero thickness are produced by embossing the fabric of the round shape 5, sufficiently so that at the level of the embossings, there is no deposit of cellulose fibers.

If the two layers of paper are produced in flat table installations, the strip 16 can be tracing paper obtained by a thorough refining of the cellulose fibers.

Printed patterns 15 can be deposited opposite the zones 18. It is also possible to deposit layers of fluorescent pigments, layers or prints of iridescent pigments, metallic prints, holograms. There will then be a sheet of paper comprising a transparent zone in transmitted light, this zone being of large surface. If a layer, for example an iridescent layer, is deposited on the transparent zone, this layer only partially covering the transparent zone, there will be an additional visual effect. In addition, such a sheet will be very difficult to reproduce by color photocopier because the iridescent area will not be reproduced by copying and the transparent area will be opaque after copying.

In FIG. 7 is shown a security paper, preferably a paper for checks, obtained according to the method according to the invention. This security paper 19 comprises at least one zone 20 whose thickness is less than the thickness of the rest of the sheet. Thus, if one writes on zone 20, the amount of the check, in case a counterfeiter tries to scratch this zone 20, he will pierce the security paper. Preferably, the zone 20 has a thickness 40% less than the thickness of the rest of the sheet.

Claims

1. Sheet of security paper comprising at least one zone of reduced opacity (3, 20), namely an area having a uniform average opacity less than the opacity of the rest of the sheet, the area having an area of at least minus 0.4 cm ² , characterized in that the zone has a reduced opacity due to the reduction of its thickness e ₂ compared to the thickness e-, of the rest of the sheet and of the fact that it has undergone additional transparency.

2. Sheet according to claim 1, characterized in that the zone of reduced opacity has a uniform average opacity less than at least 40% compared to the opacity of the rest of the sheet.

3. Sheet according to any one of claims 1 or 2, characterized in that it comprises in a part of the zone of reduced opacity a security element (15) such as a hologram, an iridescent coating, a printing to using conventional inks or inks containing colored pigments, fluorescent pigments, luminescent pigments, photochromic compounds, piezooptics, piezochroes.

4. Sheet according to any of the preceding claims, characterized in that it is onojet, comprising an area (3) whose thickness e ₂ is not zero, the residual thickness being chemically transparentized.

5. Sheet according to any one of claims 1 to 3, characterized in that it is a bijet sheet (16, 17), consisting of a first jet (17) comprising an area whose thickness is zero, and d 'a second jet (16) partially or completely transparentized.

6. Sheet according to claim 5, characterized in that the second jet (16) is completely transparentized and obtained according to the tracing paper technique, from a suspension of very refined cellulose fibers.

7. Sheet according to claim 5, characterized in that the second jet (16) is partially transparentized chemically in an area which comes into correspondence with the zone (18) of zero thickness of the first jet (17).

8. A method of manufacturing a sheet of paper comprising at least one region having a thickness reduced compared to the thickness of the rest of the sheet, characterized in that:

- a first layer (3) of paper is formed on a canvas of a first wet part of a paper machine,

- a second layer (5) of paper is formed on a canvas of a second wet part of a paper machine,

- One of the two layers of paper having at least local regions (8) of smaller thickness, so that the thickness e ₂ of the two layers of paper in said regions is up to 80% relative to the thickness (e _t ) of the rest of the sheet, - the two layers are combined and dried,

- Optionally, one or partially of one of the regions (8) of reduced thickness is made transparent.

9. Method according to claim 10, characterized in that one of the two layers has local regions (8) of zero thickness.

10. A method according to claim 8 or 9, characterized in that the method is such that the regions (8) of smaller thickness in the paper layer or layers are produced by embossed regions in relief on the metal fabric, where it follows that the deposition of fibers in these regions is reduced or completely prohibited.

11. Method according to one of claims 8 to 10, characterized in that preferably at least one of the two layers of paper is produced by a machine with a round shape.

12. Method according to one of claims 8 to 11, characterized in that the regions (8) of thinner thickness of the paper strips are formed in the form of a simple geometric pattern, in particular in the form of approximately rectangular flat regions , round or elliptical.

13. Sheet obtained by the method according to one of claims 8 to 11.

14. Application of a sheet according to one of claims 1 to 7 and 13 as paper for banknotes.

15. Application of a sheet according to one of claims 1 to 7 and 13 as security paper.